1. Field of the Invention
This invention relates to an insulation displacement connector, and to an assembly or electrical plug which comprises the insulation displacement connector and is used for making an electrical connection to an electrical cable.
2. Introduction to the Invention
Elongate cables such as power cords, grounded power leads, or heating cables often must be electrically connected to another elongate cable or to a source of electrical power such as a wall outlet. An electrical plug is frequently used to make connection to a power source. Connection of the cable to the connector or the plug can require tedious and craft-sensitive assembly, as well as the use of special tools, in order to ensure that good electrical connection is achieved.
Elongate heating cables are one type of cable which often requires connection to a connector or a plug. Such heating cables are known for use in the freeze protection and temperature maintenance of pipes. Particularly useful elongate heating cables comprise (a) first and second elongate electrodes, (b) a plurality of resistive heating elements connected in parallel between said electrodes, e.g. a continuous strip of a conductive polymer in which the electrodes are embedded or which is wrapped around the electrodes, and (c) an insulating jacket, composed, for example of an insulating polymer, which surrounds the electrodes and heating elements. In addition, the heating cable often also comprises a metallic grounding layer, in the form of a braid or a tape, surrounding the insulating jacket, which serves to electrically ground the heating cable and provides abrasion resistance. The heating cable may be cut to the appropriate length for each application, and connection must then be made to the connector or plug.
Conventional connectors and electrical plugs for use with electrical cables such as heating cables often require that, prior to installation of the cable into the plug, the conductive polymer must be stripped from the electrodes. Such an electrical plug is disclosed in U.S. Pat. Nos. 5,002,501 (Tucker) and 5,004,432 (Tucker). Stripping the polymer can be difficult, may require special tools, and may not result in completely "clean" electrodes, thus making good electrical connection to the plug difficult. In addition, the time required to strip the polymer and assemble the plug can be relatively high. Other conventional plugs do not require that the cable be stripped prior to insertion into the plug. U.S. Pat. No. 5,252,081 (Hart) discloses a plug in which connection to the electrodes is made with conductive piercing means which penetrate the insulating jacket and the conductive polymer, thus contacting the electrodes. In order to make adequate contact, it is necessary that the piercing means, e.g. screws, be sufficiently tightened. In addition, it is important that the dimensional tolerance be precise to ensure that the screws directly contact the electrodes and maintain good electrical connection even after creep and/or aging of the polymer and electrodes. U.S. Pat. No. 5,718,600 (D'Amario et al) discloses another plug which does not require stripping of the polymer prior to insertion, but which uses a rotating cutting element located inside the plug housing to cut and remove polymer from the electrodes. Rotation of the cutting element also forces the electrodes into physical contact with electrical contacts. U.S. Pat. No. 5,756,972 (Vranicar et al) discloses a connector in which a cable is inserted into a housing and connection is made to a second cable. Insulation displacement connectors are used to make connection to the unstripped cables. The disclosure of each of these patents is incorporated herein by reference.